1. Field of the Invention
The present invention relates to a transmitting device, a receiving device, a circuit device, a communication method, and a program. The present invention relates more specifically, to a transmitting device in which coupling is present between the transmitting device and a receiving device with which it is capable of communicating, a receiving device, a circuit device, a communication method executed by the transmitting device and the receiving device, and a computer program product able to realize the transmitting device.
2. Description of the Related Art
There are growing demands for higher speed wireless communication in order to send and receive rich content such as movies in real time, and realize seamless connections with wired communication. In order to realize such high-speed, high-capacity data communication, there are great expectations for millimeter-wave wireless communication techniques which are able to realize high-speed wireless communication at a data rate on the order of gigabytes per second.
Wireless communication devices typically include a digital processing unit (baseband) responsible for digital signal processing, and an analog processing unit (RF: radio frequency) responsible for analog signal processing. These processing units are connected to each other using alternating-current coupling (capacitive coupling) in order to absorb the difference in input/output bias voltage and realize stable operation.
Alternating-current coupling requires a direct-current balance, and accurate data transmission is difficult when there is a large number of direct-current components and low-frequency components. Because the bit bias in transmitted signals causes direct-current offset components, a scrambler and a data encoding technique are typically used to perform preprocessing which sufficiently diffuses the transmitted bits and eliminates the bias.
In the data encoding technique, additional bits are inserted at the expense of reducing the encoding efficiency. A scrambler used alone seems at first to have uniformly dispersed the bits, but a bias sometimes occurs as a result of the scrambling. In other words, it is possible to continuously generate the same bit over a short period of time using a scrambler, but a bit bias occurs stochastically. Direct-current offset components occur during this short period of time, and this causes the error rate to deteriorate.
If binary digital signals are being handled, this can not be a problem even when there are direct-current offset components. However, because high-speed communication techniques such as millimeter-wave communication has such a high data rate, a modulation scheme that modulates the amplitude such as 16QAM is employed, and the effect of direct-current offset components on multilevel decisions in the direction of the amplitude cannot be ignored. When the signal decision boundary is even finer, such as 64QAM, the effect of direct-current offset components is significant.
Many techniques used to compensate for direct-current offsets in wireless communication are known. Examples include Japanese Translation of PCT Application No. 2011-507408 (Patent Literature 1), Japanese Translation of PCT Application No. 2009-510948 (Patent Literature 2), Japanese Patent No. 4,195,193 (Patent Literature 3), and Japanese Laid-open Patent Publication No. 2006-86768 (Patent Literature 4). Patent Literature 1 through Patent Literature 4 relate to techniques which compensate for direct-current offsets on the receiving end. A technique has been disclosed in Japanese Laid-open Patent Publication No. 2010-45596 (Patent Literature 5) which corrects for carrier leakage that occurs in the quadrature modulation unit of a wireless communication device.
Various techniques used to compensate for direct-current offsets are known, and Patent Literature 1 through Patent Literature 4 are signal correcting techniques employed by a receiver. At the high data rates of millimeter-wave wireless communication, the overhead is too high to realize sufficient direct-current offset correction using signal correction processing on the receiving end. Patent Literature 2 and Patent Literature 3 address DC offsets due to local oscillator leakage and circuit imbalances. The technique disclosed in Patent Literature 5 addresses DC offsets due to carrier leakage in an IQ mixer. These techniques do not solve the problem of direct-current offsets due to leakage in alternating-current coupling described above.
Therefore, the development of a technique is desired which allows a transmitting device to rapidly compensate for short-term direct-current offsets and low-frequency components caused by the alternating-current coupling described above.